Rough anti-stiction layer for mems device

ABSTRACT

The present disclosure relates to a MEMS package with a rough metal anti-stiction layer, to improve stiction characteristics, and an associated method of formation. In some embodiments, the MEMS package includes a MEMS IC bonded to a CMOS IC. The CMOS IC has a CMOS substrate and an interconnect structure disposed over the CMOS substrate. The interconnect structure includes a plurality of metal layers disposed within a plurality of dielectric layers. The MEMS IC is bonded to the CMOS IC, enclosing a cavity between the MEMS IC and the CMOS IC and a moveable mass arranged in the cavity. The MEMS package further includes an anti-stiction layer disposed under the moveable mass. The anti-stiction layer is made of metal and has a rough top surface.

REFERENCE TO RELATED APPLICATION

This Application is a Continuation of U.S. application Ser. No.15/006,301 filed on Jan. 26, 2016, the contents of which are herebyincorporated by reference in their entirety.

BACKGROUND

Microelectromechanical systems (MEMS) devices, such as accelerometers,pressure sensors and gyroscopes, have found widespread use in manymodern day electronic devices. For example, MEMS accelerometers arecommonly found in automobiles (e.g., in airbag deployment systems),tablet computers or in smart phones. For many applications, MEMS devicesare electrically connected to application-specific integrated circuits(ASICs) to form complete MEMS systems.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1A illustrates a cross-sectional view of some embodiments of amicroelectromechanical systems (MEMS) package with a rough metalanti-stiction layer.

FIG. 1B illustrates a cross-sectional view of some embodiments of anenlarged portion of the MEMS package of FIG. 1A.

FIG. 1C illustrates a perspective view of some embodiments of a portionof the MEMS package of FIG. 1A.

FIG. 2 illustrates a cross-sectional view of some other embodiments of aMEMS package with a rough metal anti-stiction layer.

FIGS. 3-11 illustrate a series of cross-sectional views of someembodiments of a method for manufacturing a MEMS package with a roughmetal anti-stiction layer at various stages of manufacture.

FIG. 12 illustrates a flow diagram of some embodiments of a method formanufacturing a MEMS package with a rough metal anti-stiction layer.

DETAILED DESCRIPTION

The present disclosure provides many different embodiments, or examples,for implementing different features of this disclosure. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Some microelectromechanical systems (MEMS) devices, such asaccelerometers and gyroscopes, comprise a moveable mass and aneighboring fixed electrode plate arranged within a cavity. The moveablemass is moveable or flexible with respect to the fixed electrode platein response to external stimuli, such as acceleration, pressure, orgravity. A distance variation between the moveable mass and the fixedelectrode plate is detected through the capacitive coupling of themoveable mass and the fixed electrode plate and transmitted to ameasurement circuit for further processing.

Due to the moveable or flexible parts, MEMS devices have severalproduction challenges that are not encountered with CMOS circuits. Onesignificant challenge with MEMS devices is surface stiction. Surfacestiction refers to the tendency of a moveable or flexible MEMS part tocome into contact with a neighboring surface and “stick” to theneighboring surface. This “stiction” can occur at the end ofmanufacturing, such that the moveable or flexible part is not quitereleased from the neighboring surface, or can occur during normaloperation when the component suddenly becomes “stuck” to the neighboringsurface. As feature sizes shrink for successive generations oftechnology, surface stiction is becoming an increasingly importantconsideration in MEMS devices. Surface stiction can arise due to any oneof several different effects, such as capillary force, molecular van derWaals force or electrostatic forces between neighboring surfaces. Theextent to which these effects cause stiction can vary based on manydifferent factors such as temperature of the surfaces, contact areabetween the surfaces, contact potential difference between the surfaces,whether the surfaces are hydrophilic or hydrophobic, and so on.Approaches have been used to attempt to limit surface stiction, forexample, performing surface treatment or coating to the moveable mass orcavity surfaces to change hydrophilic properties of the surfaces.However, these approaches are difficult to integrate with variousmanufacturing processes and introduce contamination.

The present application is related to a MEMS package with a rough metalanti-stiction layer to improve stiction characteristics, and associatedmethods of forming such a MEMS package. The MEMS package comprises aMEMS IC bonded to a CMOS IC. An anti-stiction layer is disposed on theCMOS IC under a moveable mass of the MEMS IC. The anti-stiction layerhas a rough top surface made up of a series of peaks and valleys. Thesepeaks and valleys, which limit the overall contact area to points wherethe peaks of the anti-stiction layer meet a lower surface of themoveable mass, help improve stiction characteristics. Therefore,stiction can be avoided at the end of the manufacturing process and/orduring normal operation of the MEMS package, and reliability isaccordingly improved. The concept will be illustrated herein withregards to some example MEMs devices, but it will be appreciated thatthe concept is applicable to suitable MEMS device employing moveableparts, including actuators, valves, switches, microphones, pressuresensors, accelerators, and/or gyroscopes, for example.

FIG. 1A illustrates a cross-sectional view of some embodiments of a MEMSpackage 100 with a rough metal anti-stiction layer. The MEMS package 100comprises a CMOS IC 102 comprising CMOS devices disposed within a CMOSsubstrate 104 and a MEMS IC 112 bonded to the CMOS IC 102. The MEMS IC112 comprises a MEMS device layer 130 bonded the CMOS IC 102. The MEMSdevice layer 130 comprises a fixed portion 132 and a moveable mass 116.In some embodiments, the moveable mass 116 is connected to the fixedportion 132 by one or more cantilever beams or springs (not shown) andat least a portion of the moveable mass 116 can move in at least onedirection with respect to the fixed portion 132. In some embodiments,the CMOS substrate 104 and the MEMS device layer 130 may comprisemonocrystalline silicon. The MEMS device layer 130 is bonded to the CMOSsubstrate 104, enclosing a cavity 120 between the moveable mass 116 andthe CMOS substrate 104. The moveable mass 116 is arranged in the cavity120. An anti-stiction layer 110 is disposed over the CMOS substrate 104and under the moveable mass 116. The anti-stiction layer 110 has a roughtop surface 110 s, which is configured to limit contact area to a lowersurface 116 s of the moveable mass 116 when the moveable mass 116 movesdownwardly to reach the anti-stiction layer 110. Thus stiction islimited.

In some embodiments, a fixed electrode plate 106 is disposed over theCMOS substrate 104 between portions of the anti-stiction layer 110. Ameasurement circuit is configured to detect a distance change betweenthe moveable mass 116 and the fixed electrode plate 106, for examplebased on changes of a varying current or voltage measured between themoveable mass 116 and the fixed electrode plate 106. Compared to theanti-stiction layer 110, the fixed electrode plate 106 has a smooth topsurface 106 s. An uppermost region of the rough top surface 110 s isspaced apart from the lower surface 116 s of the moveable mass 116 by afirst vertical distance d₁, and an uppermost region of the smooth topsurface 106 s is spaced apart from the lower surface 116 s of themoveable mass 116 by a second vertical distance d₂ that is greater thanthe first vertical distance d₁. In this way, the anti-stiction layer 110prevents the moveable mass 116 from reaching and “sticking” to the fixedelectrode plate 106. In some embodiments, the smooth top surface 106 shas a surface height from a bottom surface of the fixed electrode plate106 that is substantially same as a mean surface height of the rough topsurface 110 s. The mean surface height of the rough top surface 110 s isa height from a mean surface 122 s of the rough top surface 110 s to abottom surface of the anti-stiction layer 110. The height of the meansurface 122 s is calculated from the roughness profile. In someembodiments, the anti-stiction layer 110 and the fixed electrode plate106 comprise the same metal material and have the bottom surfacessubstantially aligned one another. In some other embodiments, theanti-stiction layer 110 and the fixed electrode plate 106 canalternatively be made of different materials from one another. In someembodiments, the anti-stiction layer 110 may comprise aluminum (Al),nickel (Ni) or copper (Cu).

FIG. 1B illustrates a cross-sectional view of some embodiments of anenlarged portion of the MEMS package 100 of FIG. 1A. As shown in moredetail in FIG. 1B, the rough top surface 110 s of the anti-stictionlayer 110 faces the lower surface 116 s of the moveable mass 116 and hasa series of peaks (e.g., 124) and valleys (e.g., 126), that reducecontact area between the moveable mass 116 and the anti-stiction layer110. Thus, stiction force between the moveable mass 116 andanti-stiction layer 110 is decreased and the possibility of stiction isreduced. In some embodiments, the rough top surface 110 s ofanti-stiction layer 110 has a root mean square (RMS) surface roughnessin a range of from about 10 nm to about 60 nm, preferably greater than40 nm. The RMS surface roughness is calculated as the root mean squareof a surface's measured microscopic peaks and valleys, as provided bythe formula below:

${R_{q} = \sqrt{\frac{1}{n}{\overset{n}{\sum\limits_{i = 1}}y_{i}^{2}}}};$

wherein R_(q) is the RMS surface roughness of the anti-stiction layer110, y_(i) is the vertical distance from the mean surface 122 to each ofn data points, which can be spaced at regular intervals on the meansurface 122. In some embodiments, a distance d_(s) between the rough topsurface 110 s of the anti-stiction layer 110 and the lower surface 116 sof the moveable mass 116 is less than 100 μm, for example, between about10 μm and about 20 μm, such that stiction could be a consideration thatmay affect yield and performance of the MEMS package 100.

FIG. 1C illustrates a perspective view of some embodiments of a portionof the MEMS package 100 of FIG. 1A. As shown in FIG. 1C, theanti-stiction layer 110 can have a ring shape surrounding the fixedelectrode plate 106. The anti-stiction layer 110 can also be one or aplurality of rectangular, round or other suitable shaped portionsdisposed alongside the fixed electrode plate 106. During operation ofthe MEMS package 100, the moveable mass 116 can move with respect to theCMOS substrate 104 commensurate with a force experienced by the MEMSpackage 100. For example, if the MEMS package 100 is moved upwardsuddenly, the moveable mass 116 will tend to stay at rest such that themoveable mass 116 and CMOS substrate 104 will squeeze closer togetherduring the acceleration. This temporary change in spacing due to theacceleration correspondingly provides a temporary change in acapacitance between the moveable mass 116 and the fixed electrode plate106. The capacitance between the fixed electrode plate 106 and moveablemass 116 can be monitored, and the acceleration experienced by the MEMSdevice can then be calculated based on this monitored capacitance. Insome cases, the acceleration is extreme that the lower surface 116 s ofthe moveable mass 116 moves very close and may even reach on the roughtop surface 110 s of the anti-stiction layer 110. Since the peaks (see124 in FIG. 1B) of the rough top surface 110 s are closer to themoveable mass 116 than the smooth top surface 106 s, the anti-stictionlayer 110 prevents the fixed electrode plate 106 from contacting themoveable mass 116. Thereby, stiction between the fixed electrode plate106 and the moveable mass 116 is limited. Further, compared to the roughtop surface 116 s which provides good mechanical anti-stictionproperties, the smooth top surface 106 s of the fixed electrode plate106 provides good electrical properties for MEMS devices over differentICs in that the smoothness helps provide a consistent distance betweenthe fixed electrode plate 106 and the lower surface of the moveablemass.

FIG. 2 illustrates a cross-sectional view of some other embodiments of aMEMS package 200 with a rough metal anti-stiction layer. The MEMSpackage 200 comprises a CMOS IC 202 including a CMOS substrate 204 andan interconnect structure 232 disposed over the CMOS substrate 204. Theinterconnect structure 232 includes a plurality of metal layers disposedwithin a plurality of ILD layers. A MEMS IC 212 is bonded to an uppersurface 232 s of the interconnect structure 232 and, in cooperation withthe CMOS IC 202, enclosing a cavity 220 between the MEMS IC 212 and theCMOS IC 202. A moveable mass 216 of the MEMS IC 212 is arranged withinthe cavity 220.

In some embodiments, the MEMS IC 212 further comprises a cappingsubstrate 214 having a recess 222 disposed directly above the moveablemass 216 and which constitutes a portion of the cavity 220 in fluidcommunication with a lower portion between the moveable mass 216 and theCMOS IC 202. The cavity 220 is hermetically sealed from the ambientenvironment surrounding the MEMS package 200. In other embodiments, thecapping substrate 214 encloses the recess 222 in cooperation with themoveable mass 216 to form a second hermetically sealed cavity that isisolated from the cavity 220 having the same or different pressures. Themoveable mass 216 can be a flexible MEMS membrane, and/or other MEMSstructures, configured to deflect in proportion to external stimuli,such as pressure, acceleration, etc.

An anti-stiction layer 210 is disposed on the upper surface 232 s of theinterconnect structure 232 under the moveable mass 216. In someembodiments, the anti-stiction layer 210 is made of metal and has arough top surface. The MEMS package 200 may further comprise a fixedelectrode plate 206 disposed on the upper surface 232 s of theinterconnect structure 232 under the moveable mass 216, coupled to ameasurement circuit configured to detect a distance change between themoveable mass 216 and the fixed electrode plate 206 through capacitivecoupling of the moveable mass 216 and the fixed electrode plate 206. Insome embodiments, the fixed electrode plate 206 is made of the samemetal as the anti-stiction layer 210 but has a smooth top surface.

In some embodiments, the MEMS package 200 further comprises a bondingstructure 224 disposed between the MEMS IC 212 and the CMOS IC 202,configured to bond the two together. In some embodiments, the bondingstructure 224 can be a semiconductor-to-metal bonding structure where afirst bonding pad 208 of the CMOS IC 202 comprises a metal material suchas Al, Cu, Ti, Ta, Au, Ni, Sn and a second bonding pad 218 of the MEMSIC 212 comprises a semiconductor material such as Ge, Si, SiGe. In someother embodiments, the bonding structure 224 can be a eutectic bondingstructure and the first bonding pad 208 and the second bonding pad 218each including at least one of Al, Cu, Ti, Ta, Au, Ni, Sn, or anothermetal. As an example, the first bonding pad 208 can comprise aluminumand the second bonding pad 218 can comprise germanium. In someembodiments, the first bonding pad 208 or the second bonding pad 218 canbe a conformal layer lining a protrusion portion of the CMOS IC 202 orthe MEMS IC 212. The first bonding pad 208 can be disposed on the uppersurface 232 s of the interconnect structure 232 and comprise the samemetal with a substantially same thickness of anti-stiction layer 210. Insome embodiments, the upper surface 232 s of the interconnect structure232 is a top surface of a top ILD layer 228 surrounding a top metallayer 226 as shown in FIG. 2. The first bonding pad 208 and the fixedelectrode plate 206 can be respectively coupled to the CMOS devices ofthe CMOS IC 202 through metal lines of the top metal layer 226. In someembodiments, an additional dielectric layer 230 is disposed over the topILD layer 228 and surrounds the first bonding pad 208. In someembodiments, the bonding structure 224 can have a ring-likeconfiguration as viewed from top, and the first and second bonding pads208, 218 can laterally surround the cavity 220. In some otherembodiments, the first bonding pad 208, the anti-stiction layer 210 andthe fixed electrode plate 206 are disposed aligned within an uppermostmetallization plane of the interconnect structure 232.

In some embodiments, the CMOS substrate 204, or the capping substrate214 may comprise bulk semiconductor substrates including one or more of,for example, silicon, germanium, silicon carbide, a group III element,and a group V element. In other embodiments, the CMOS substrate 204 orthe capping substrate 214 are semiconductor-on-insulator (SOI)substrates, such as silicon-on-insulator or polysilicon-on-insulator(POI) substrates, for example.

Therefore, as can be seen from the above embodiments, a rough metalanti-stiction layer can be advantageous in reducing stiction in MEMSstructures. The precise surface roughness that is present for the metalanti-stiction layer can vary depending on the manufacturing processesand conditions, such as annealing temperature and time, but typicallyexhibit a rough surface of peaks and valleys. These peaks and valleysare often irregular, with the depths and widths of the valleys varyingover a length or area of the surface, and/or the height and widths ofthe peaks also varying over a length or area of the surface. Aside fromadvantageously limiting stiction, metal anti-stiction layer is simple toincorporate into modern semiconductor manufacturing process, and iscompatible with other MEMS materials (e.g. bulk silicon). It also avoidscontamination problem of the other anti-stiction coatings.

FIGS. 3-11 illustrate a series of cross-sectional views of someembodiments of a method for manufacturing a MEMS package with a roughmetal anti-stiction layer at various stages of manufacture.

As shown in cross-sectional view 300 of FIG. 3, a CMOS IC 202, whichincludes an interconnect structure 232 over a CMOS substrate 204, isprovided. A plurality of CMOS devices are formed within the CMOSsubstrate 204. In various embodiments, the CMOS substrate 204 maycomprise any type of semiconductor body (e.g., silicon/CMOS bulk, SiGe,SOI, etc.) such as a semiconductor wafer or one or more die on a wafer,as well as any other type of semiconductor and/or epitaxial layersformed thereon and/or otherwise associated therewith. In someembodiments, the interconnect structure 232 may be formed by forming oneor more dielectric layers such as inter-layer dielectrics (ILD) over afront surface of the CMOS substrate 204. The ILD layers are subsequentlyetched to form via holes and/or metal trenches. The via holes and/ormetal trenches are then filled with a conductive material to form aplurality of metal layers. In some embodiments, the ILD layers may bedeposited by a physical vapor deposition technique (e.g., PVD, CVD,etc.). The plurality of metal layers may be formed using a depositionprocess and/or a plating process (e.g., electroplating, electro-lessplating, etc.). In various embodiments, the plurality of metal layersmay comprise tungsten, copper, or aluminum copper, for example. In someembodiments, a top metal layer 226 of the plurality of metal layers hasan upper surface aligned with an upper surface of the top ILD layer 228of the plurality of ILD layers.

As shown in cross-sectional view 400 of FIG. 4, a metal layer 402 isformed over the CMOS IC 202. In some embodiments, the metal layer isformed directly on the upper surfaces of the top metal layer 226 and thetop ILD layer 228. In some embodiments, the metal layer is formed by achemical vapor deposition process, such as low pressure chemical vapordeposition (LPCVD), plasma-enhanced chemical vapor deposition (PECVD) oran atmospheric pressure chemical vapor deposition (APCVD) growthprocess. In some embodiments, the metal layer may comprise aluminum(Al), nickel (Ni) or copper (Cu).

As shown in cross-sectional view 500 of FIG. 5, the metal layer 402 ispatterned to form an anti-stiction precursor 502, a fixed electrodeplate 206 and a first bonding pad 208. An additional dielectric layer230 can be formed to surround the first bonding pad 208.

As shown in cross-sectional view 600 of FIG. 6, an amorphous siliconlayer 602 is formed on exposed surfaces of the interconnect structureand the patterned metal layer. In some embodiments, the amorphoussilicon layer 602 is formed by a chemical vapor deposition process, suchas low pressure chemical vapor deposition (LPCVD), plasma-enhancedchemical vapor deposition (PECVD) or an atmospheric pressure chemicalvapor deposition (APCVD) growth process. For example, the amorphoussilicon layer 602 can be formed by a PECVD process at a temperaturelower than about 400° C.

As shown in cross-sectional view 700 of FIG. 7, the amorphous siliconlayer 602 is patterned to leave a portion 702 on the anti-stictionprecursor 502 and to remove remaining portions such as a second portionof the amorphous silicon layer 602 on the fixed electrode plate 206.

As shown in cross-sectional view 800 of FIG. 8, an annealing process isperformed to facilitate inter-diffusion between the portion 702 of theamorphous silicon layer and the anti-stiction precursor 502 such thatthe anti-stiction precursor 502 converts to an anti-stiction layer 210with a rough top surface. Metal silicide micro-particles can be formedat an interface of the anti-stiction layer 210 and the portion 702 ofthe amorphous silicon layer through a granulation process of theanti-stiction precursor 502 at applicable temperatures. The size,density, and the composition of the micro-particles could be controlledby adjusting the annealing temperature, time, and the film thickness. Asan example, the anti-stiction layer 210 can be made of aluminum and beannealed at a temperature of about 430° C. for about 1 hour. A diameterof the formed micro-particles can be in a range of about several tens ofnanometers.

As shown in cross-sectional view 900 of FIG. 9, an etching process isperformed to remove the portion 702 of the amorphous silicon layer andto leave a rough top surface of the anti-stiction layer 210 exposed. Insome embodiments, the portion 702 of the amorphous silicon layer isremoved by a selective etching process such as a Reactive Ion Etching(RIE) process, for example.

As shown in cross-sectional view 1000 of FIG. 10, a MEMS IC 212 isprovided. In some embodiments, a MEMS device layer 1002 is etched backfrom a front side to form a protrusion 1004 at a position to be bondedto the CMOS IC. A second bonding pad 218 is formed on the protrusion1004. In some embodiments, the second bonding pad 218 is formedconformally covering sidewalls of the protrusion 1004. In someembodiments, a capping substrate 214 is bonded to the MEMS device layer1002 at a back side that is opposite to the protrusion 1004. The cappingsubstrate 214 can be prepared from a bulk semiconductor wafer 302including, for example, a monocrystalline wafer, or another substratemade of germanium, silicon carbide, a group III element, and/or a groupV element, for example. In some embodiments, a recess 222 can be etchedto a proper depth at a location corresponding to moveable or flexibleportion of the MEMS device layer. Notably, among other considerations,applicable heights of the protrusion 1004 and the recess 222 are formedwith a consideration of providing sufficient space for motion and/orsuitable stiction force between a moveable or flexible part of the MEMSdevice to be formed and a neighboring component. The MEMS device layer1002 is patterned to form MEMS devices including a moveable mass 216.The MEMS devices include, for example, micro-actuators or micro-sensorssuch as a micro-valve, a micro-switch, a microphone, a pressure sensor,an accelerator, a gyroscope or any other device having a moveable orflexible part that moves or flexes with respect to the fixed portion.

As shown in cross-sectional view 1100 of FIG. 11, the MEMS IC 212 isbonded to the CMOS IC 202. A cavity 220 is enclosed between the moveablemass 216 and the fixed electrode plate 206. In some embodiments, theMEMS IC 212 and the CMOS IC 202 are bonded by semiconductor-to-metalbonding where the first bonding pad 208 comprises metal materials suchas Al, Cu, Ti, Ta, Au, Ni, Sn and the second bonding pad 218 comprisessemiconductor materials such as Ge, Si, SiGe. In some other embodiments,the MEMS IC 212 and the CMOS IC 202 are bonded by eutectic bondingbetween two metal materials each including at least one of Al, Cu, Ti,Ta, Au, Ni, Sn, or another metal. The materials to be bonded are pressedagainst each other in an annealing process to form a eutectic phase ofthe materials. For example, a eutectic bonding between Ge and Al isformed at an annealing temperature in a range from 400° C. to 450° C.After the MEMS IC 212 is bonded to the CMOS IC 202, the MEMS package isformed when the bonded CMOS IC 202 and MEMS IC 212, which are oftenbonded at the wafer level, are diced into separate chips after bonding.

FIG. 12 illustrates a flow diagram of some embodiments of a method formanufacturing a MEMS package with a rough metal anti-stiction layer.

While disclosed method 1200 is illustrated and described herein as aseries of acts or events, it will be appreciated that the illustratedordering of such acts or events are not to be interpreted in a limitingsense. For example, some acts may occur in different orders and/orconcurrently with other acts or events apart from those illustratedand/or described herein. In addition, not all illustrated acts may berequired to implement one or more aspects or embodiments of thedescription herein. Further, one or more of the acts depicted herein maybe carried out in one or more separate acts and/or phases

At 1202, a CMOS IC is provided. CMOS devices are formed within a CMOSsubstrate and an interconnect structure including a plurality of metallayers formed within a plurality of ILD layers is formed over the CMOSsubstrate. FIG. 3 illustrates a cross-sectional view corresponding tosome embodiments corresponding to act 1202.

At 1204, a metal layer is formed over the CMOS IC. In some embodiments,the metal layer is formed directly on an upper surface of theinterconnect structure. FIG. 4 illustrates a cross-sectional viewcorresponding to some embodiments corresponding to act 1204.

At 1206, the metal layer is patterned to form an anti-stictionprecursor, a fixed electrode plate, and a first bonding pad. FIG. 5illustrates a cross-sectional view corresponding to some embodimentscorresponding to act 1206.

At 1208, an amorphous silicon layer is formed over the patterned metallayer. In some embodiments, the amorphous silicon layer can be formed bya PECVD process. FIG. 6 illustrates a cross-sectional view correspondingto some embodiments corresponding to act 1208.

At 1210, the amorphous silicon layer is patterned to leave a portion onthe anti-stiction layer and to remove remaining portions of theanti-stiction layer. FIG. 7 illustrates a cross-sectional viewcorresponding to some embodiments corresponding to act 1210.

At 1212, an annealing process is performed. The annealing processfacilitates inter-diffusion between the amorphous silicon and theanti-stiction layer to form silicide micro-particles at an interface.FIG. 8 illustrates a cross-sectional view corresponding to someembodiments corresponding to act 1212.

At 1214, the amorphous silicon layer is removed. In some embodiments,the amorphous silicon layer is removed by a RIE process. After removingthe amorphous silicon layer together with the silicide micro-particles,a rough top surface of the anti-stiction layer is exposed. FIG. 9illustrates a cross-sectional view corresponding to some embodimentscorresponding to act 1214.

At 1216, a MEMS IC is provided. In some embodiments, a MEMS device layeris prepared for following bonding process by forming a protrusion and asecond bonding pad for the MEMS IC. MEMS structures are formed includingforming a moveable mass. In some embodiments, a capping substrate isbonded to a back side of the MEMS device layer. FIG. 10 illustrates across-sectional view corresponding to some embodiments corresponding toact 1216.

At 1218, the MEMS IC is bonded to the CMOS IC. A cavity can be enclosedbetween the moveable mass of the MEMS IC and the fixed electrode plateon the CMOS IC. FIG. 11 illustrates a cross-sectional view correspondingto some embodiments corresponding to act 1218.

Thus, as can be appreciated from above, the present disclosure relatesto a MEMS package with a rough metal anti-stiction layer to improvestiction characteristics, and associated methods of forming such a MEMSpackage. The MEMS package comprises a MEMS IC bonded to a CMOS IC and ananti-stiction layer is disposed on the CMOS IC under a moveable mass ofthe MEMS IC. In some embodiments, the anti-stiction layer is formed byforming an amorphous silicon layer on a metal precursor followed byperforming an annealing process. The annealing process facilitatesinter-diffusion and formation of silicide micro-particles at aninterface between the metal precursor and the amorphous silicon layer.Then the amorphous silicon is removed, together with the formed silicidemicro-particles, leaving a rough surface for the metal precursor.

In some embodiments, the present disclosure relates to a MEMS package.The MEMS package comprises a CMOS IC comprising a CMOS substrate and aninterconnect structure disposed over the CMOS substrate. Theinterconnect structure includes a plurality of metal layers disposedwithin a plurality of dielectric layers. The MEMS package furthercomprises a MEMS IC bonded to the CMOS IC, enclosing a cavity betweenthe MEMS IC and the CMOS IC and a moveable mass arranged in the cavity.The MEMS package further comprises an anti-stiction layer disposed underthe moveable mass. The anti-stiction layer is made of metal and has arough top surface.

In other embodiments, the present disclosure relates to a MEMS package.The MEMS package comprises a CMOS IC comprising CMOS devices disposedwithin a CMOS substrate and a MEMS device layer bonded to the CMOS ICand comprising a fixed portion and a moveable mass connected to thefixed portion. The MEMS package further comprises a capping substratebonded to a back side of the MEMS device layer opposite to the CMOS ICso as to enclose a cavity between the capping substrate and the CMOSsubstrate. The moveable mass is arranged in the cavity. The MEMS packagefurther comprises an anti-stiction layer disposed over the CMOSsubstrate and under the moveable mass. The anti-stiction layer has arough upper surface with a root mean square (RMS) surface roughness in arange of from about 40 nm to about 60 nm.

In yet other embodiments, the present disclosure relates to a method formanufacturing a microelectromechanical systems (MEMS) package. Themethod comprises providing a CMOS IC including CMOS devices arrangedwithin a CMOS substrate and forming and patterning a metal layer overthe CMOS substrate to form an anti-stiction layer and a fixed electrodeplate. The method further comprises forming a rough upper surface forthe anti-stiction layer and providing a MEMS IC comprising a moveablemass arranged within a recess of a MEMS substrate. The method furthercomprises bonding the CMOS IC to the MEMS IC to enclose a cavity betweenthe moveable mass and the fixed electrode plate and the anti-stictionlayer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A microelectromechanical systems (MEMS) packagecomprising: a CMOS IC comprising a CMOS substrate and an interconnectstructure disposed over the CMOS substrate, wherein the interconnectstructure includes a plurality of metal layers disposed within aplurality of dielectric layers; a MEMS IC bonded to the CMOS IC,enclosing a cavity between the MEMS IC and the CMOS IC and a moveablemass arranged in the cavity; and an anti-stiction layer disposed underthe moveable mass, wherein the anti-stiction layer is made of metal andhas a rough top surface.
 2. The MEMS package of claim 1, furthercomprising: a fixed electrode plate disposed on the upper surface of theinterconnect structure under the moveable mass and made of the samemetal as the anti-stiction layer, wherein a measurement circuit isconfigured to detect a distance change between the moveable mass and thefixed electrode plate.
 3. The MEMS package of claim 2, wherein theanti-stiction layer has a ring shape surrounding the fixed electrodeplate.
 4. The MEMS package of claim 2, wherein the fixed electrode platehas a smooth top surface, wherein the smooth top surface has a surfaceheight that is substantially same with a mean surface height of therough top surface of the anti-stiction layer.
 5. The MEMS package ofclaim 4, wherein an uppermost region of the rough top surface is spacedapart from a lower surface of the moveable mass by a first verticaldistance, and an uppermost region of the smooth top surface is spacedapart from the lower surface of the moveable mass by a second verticaldistance, the second vertical distance being greater than the firstvertical distance.
 6. The MEMS package of claim 1, wherein theanti-stiction layer comprises aluminum (Al).
 7. The MEMS package ofclaim 1, further comprising a eutectic bonding structure that includes afirst bonding pad on the CMOS IC and a second bonding pad on the MEMSIC, wherein the anti-stiction layer and the first bonding pad havesubstantially the same thickness as one another.
 8. The MEMS package ofclaim 1, wherein the rough top surface of the anti-stiction layer has aroot mean square (RMS) surface roughness in a range of from about 40 nmto about 60 nm.
 9. The MEMS package of claim 1, wherein the MEMS ICfurther comprises: a capping substrate comprising a recess which isdisposed directly above the moveable mass proximate a back side of theMEMS opposite to the CMOS IC, wherein the recess constitutes a portionof the cavity.
 10. The MEMS package of claim 9, wherein the CMOSsubstrate and the capping substrate comprise monocrystalline silicon.11. A microelectromechanical systems (MEMS) package comprising: a CMOSIC comprising CMOS devices disposed within a CMOS substrate; a MEMSdevice layer bonded to the CMOS IC and comprising a fixed portion and amoveable mass connected to the fixed portion; a capping substrate bondedto a back side of the MEMS device layer opposite to the CMOS IC so as toenclose a cavity between the capping substrate and the CMOS substrate,wherein the moveable mass is arranged in the cavity; and ananti-stiction layer disposed over the CMOS substrate and under themoveable mass.
 12. The MEMS package of claim 11, further comprising afixed electrode plate disposed over the CMOS substrate between portionsof the anti-stiction layer, wherein the anti-stiction layer and thefixed electrode plate comprise the same metal material and have bottomsurfaces that are substantially aligned to one another.
 13. The MEMSpackage of claim 11, wherein the CMOS IC comprises an interconnectstructure comprising a plurality of metal layers disposed within aplurality of dielectric layers; wherein the anti-stiction layer isdisposed on an upper surface of the interconnect structure.
 14. The MEMSpackage of claim 13, further comprising: a eutectic bonding structure ofa first bonding pad on the CMOS IC and a second bonding pad on the MEMSdevice layer; wherein the first bonding pad is disposed on the uppersurface of the interconnect structure; wherein the anti-stiction layerand the first bonding pad comprise the same metal material and havesubstantially the same thickness.
 15. The MEMS package of claim 11,wherein the anti-stiction layer comprises aluminum (Al) or copper (Cu).16. A microelectromechanical systems (MEMS) package comprising: a CMOSIC comprising CMOS devices disposed within a CMOS substrate and aninterconnect structure disposed over the CMOS substrate, wherein theinterconnect structure includes a plurality of metal layers disposedwithin a plurality of dielectric layers; a MEMS device overlying theCMOS IC and comprising a moveable mass; and a metal layer disposed on anupper surface of a top dielectric layer of the interconnect structure,and having discrete portions comprising a fixed electrode plate of theMEMS device, and an anti-stiction layer under the moveable mass of theMEMS device.
 17. The MEMS package of claim 16, wherein the anti-stictionlayer has a surface height substantially same with a surface height ofthe fixed electrode plate.
 18. The MEMS package of claim 16, wherein theanti-stiction layer comprises a rough upper surface with a root meansquare (RMS) surface roughness greater than that of the fixed electrodeplate.
 19. The MEMS package of claim 16, wherein the anti-stiction layeris disposed directly on a top surface of the interconnect structure. 20.The MEMS package of claim 16, wherein the CMOS IC and the MEMS IC arebonded through a eutectic bonding structure comprising a first bondingpad on the CMOS IC and a second bonding pad on the MEMS IC; wherein thefirst bonding pad has a thickness that is substantially the same as theanti-stiction layer.